Hyperthyroidism is also referred to as thyrotoxicosis. Primary Hyperthyroidism is characterized by elevated serum thyroxine (T4), triiodothyronine (T3), and suppressed serum TSH levels.Central (secondary) Hyperthyroidism is caused by TSH-secreting pituitary tumors secreting normal to increased amounts of TSH despite increased levels of thyroid hormone. (Huether & McCance, 2012). There are five different tests used to diagnose Hyperthyroidism or evaluate the functioning of the thyroid. All five of these studies are listed and described in further detail in Mosby's Manual of Diagnostic and Laboratory Tests text. (Pagana & Pagana, 2010). Triiodothyronine (T3)- Blood sampleThis test is used to evaluate thyroids function and diagnose Hyperthyroidism. This is the most common test preformed in diagnosis of Hyperthyroidism.Radioisotope may alter test results if RIA methods are used. T3 levels are also increased with pregnancy, use of medications such as: oral contraceptives, estrogen, and methadone. Increased levels of T3 produced even with decreased stimulation of TSH indicates Hyperthyroidism.
Thyroid scanning (thyroid scintiscan)-Used to detect the thyroids shape, size, position and function with the use of radioactive dye, most commonly Technetium-99m. A scintigraphy camera is passed over the neck area where the thyroid is located and several images are recorded. These images are used in detection of an enlarged thyroid or presence of nodules on the thyroid. This test also assists in differentiating between Graves disease and Plummer disease. Graves disease is characterized as a diffused, enlarged hyper functioning gland and Plummer's disease is characterized as a nodular hyper functioning gland. Contraindications include allergies to iodine or shellfish, if iodine is the radionuclide used. Women who are pregnant should use caution and speak with their doctors to determine if the benefits outweigh the risks of preforming this test. Radiation-induced oncogenesis can be avoided if Technetium or low-radioactive iodine isomers are used versus iodine. Foods containing iodine may affect the results due to iodine saturation by all the iodine-binding sites causing little iodine tracer to be taken up by the thyroid. Recent x-ray contrast agents can also affect the results of this test as they contain large amounts of iodine. Certain medications as such: cough meds, multiple vitamins, oral contraceptives, thyroid drugs should be restricted 6 weeks before the test is preformed. There are five simple steps to this exam: 1. Standard dose of oral radioactive Tc administered. 2. Scanning performed 24 hours after, if technetium is used, scanning may be preformed 2 hours after administration.3. The patient should be placed in a supine position with the scintigraphy camera placed over the thyroid. 4. Radioactive levels are then recorded.5. Takes less than 30 minutes to complete scan. Hyperthyroidism is diagnosed with increased amounts of radionuclide uptake.
Thyroxine (T4)- Blood SampleA blood sample of Thyroxine (T4) monitors the function of the thyroid along with the assessment of replacement and suppressive therapies. This is a direct measurement of total T4 present in the blood. Greater than normal levels indicate Hyperthyroidism.Oral contraceptives and pregnancy cause increased T4 levels along with medications such as: amphetamines, clofibrate, estrogens, heroin, iodinated contrast media, iodine, and methadone. With Hyperthyroidism the thyroid produces increased levels with lack of TSH stimulation.
Thyrotropin-releasing hormones (TRH)This study is used in the evaluation of patients with Hyperthyroidism. IV injection of TRH used to assess anterior pituitary glands secretion of TSH in response to the IV injection of TRH. With Hyperthyroidism there is a slight to no increase in TSH, pituitary TSH secretion is suppressed by the inhibitory effects of excess circulating thyroxine (T4) and triiodothyronine (T3). Due to the recent discovery of radioimmunoassay for TSH, TRH stimulation is no longer used to diagnose Hyperthyroidism. In diagnosing Hyperthyroidism the pituitary response to TRH will be decreased and baseline levels will be less than double the normal levels.
Thyroid-Stimulating Hormone (TSH)This is another blood sample that can be drawn to help detect the thyroids function. This test is no longer commonly used due to use of immunoassays which can detect extremely low levels of TSH. Indication of Hyperthyroidism results in increased levels of thyroid hormones that also inhibit the release of TSH.
Diagnosis of Hyperthyroidism:
Hyperthyroidism is also referred to as thyrotoxicosis.
Primary Hyperthyroidism is characterized by elevated serum thyroxine (T4), triiodothyronine (T3), and suppressed serum TSH levels.Central (secondary) Hyperthyroidism is caused by TSH-secreting pituitary tumors secreting normal to increased amounts of TSH despite increased levels of thyroid hormone. (Huether & McCance, 2012).
There are five different tests used to diagnose Hyperthyroidism or evaluate the functioning of the thyroid. All five of these studies are listed and described in further detail in Mosby's Manual of Diagnostic and Laboratory Tests text. (Pagana & Pagana, 2010).
Triiodothyronine (T3)- Blood sampleThis test is used to evaluate thyroids function and diagnose Hyperthyroidism. This is the most common test preformed in diagnosis of Hyperthyroidism.Radioisotope may alter test results if RIA methods are used. T3 levels are also increased with pregnancy, use of medications such as: oral contraceptives, estrogen, and methadone. Increased levels of T3 produced even with decreased stimulation of TSH indicates Hyperthyroidism.
Thyroid scanning (thyroid scintiscan)-Used to detect the thyroids shape, size, position and function with the use of radioactive dye, most commonly Technetium-99m. A scintigraphy camera is passed over the neck area where the thyroid is located and several images are recorded. These images are used in detection of an enlarged thyroid or presence of nodules on the thyroid. This test also assists in differentiating between Graves disease and Plummer disease. Graves disease is characterized as a diffused, enlarged hyper functioning gland and Plummer's disease is characterized as a nodular hyper functioning gland.
Contraindications include allergies to iodine or shellfish, if iodine is the radionuclide used. Women who are pregnant should use caution and speak with their doctors to determine if the benefits outweigh the risks of preforming this test. Radiation-induced oncogenesis can be avoided if Technetium or low-radioactive iodine isomers are used versus iodine. Foods containing iodine may affect the results due to iodine saturation by all the iodine-binding sites causing little iodine tracer to be taken up by the thyroid. Recent x-ray contrast agents can also affect the results of this test as they contain large amounts of iodine. Certain medications as such: cough meds, multiple vitamins, oral contraceptives, thyroid drugs should be restricted 6 weeks before the test is preformed.
There are five simple steps to this exam:
1. Standard dose of oral radioactive Tc administered. 2. Scanning performed 24 hours after, if technetium is used, scanning may be preformed 2 hours after administration.3. The patient should be placed in a supine position with the scintigraphy camera placed over the thyroid. 4. Radioactive levels are then recorded.5. Takes less than 30 minutes to complete scan.
Hyperthyroidism is diagnosed with increased amounts of radionuclide uptake.
Thyroxine (T4)- Blood SampleA blood sample of Thyroxine (T4) monitors the function of the thyroid along with the assessment of replacement and suppressive therapies. This is a direct measurement of total T4 present in the blood. Greater than normal levels indicate Hyperthyroidism.Oral contraceptives and pregnancy cause increased T4 levels along with medications such as: amphetamines, clofibrate, estrogens, heroin, iodinated contrast media, iodine, and methadone.
With Hyperthyroidism the thyroid produces increased levels with lack of TSH stimulation.
Thyrotropin-releasing hormones (TRH)This study is used in the evaluation of patients with Hyperthyroidism. IV injection of TRH used to assess anterior pituitary glands secretion of TSH in response to the IV injection of TRH. With Hyperthyroidism there is a slight to no increase in TSH, pituitary TSH secretion is suppressed by the inhibitory effects of excess circulating thyroxine (T4) and triiodothyronine (T3). Due to the recent discovery of radioimmunoassay for TSH, TRH stimulation is no longer used to diagnose Hyperthyroidism. In diagnosing Hyperthyroidism the pituitary response to TRH will be decreased and baseline levels will be less than double the normal levels.
Thyroid-Stimulating Hormone (TSH)This is another blood sample that can be drawn to help detect the thyroids function. This test is no longer commonly used due to use of immunoassays which can detect extremely low levels of TSH. Indication of Hyperthyroidism results in increased levels of thyroid hormones that also inhibit the release of TSH.